Platform support changes

Classes / members marked as obsolete

* #1124 Mark NullableValueConverter as obsolete since converter doesn’t have a target type, so this converter won’t work as expected NullableValueConverter
* #1209 Mark IStartupInfoProvider as obsolete in favor of Orc.CommandLine since that implementation takes better care of supporting different quote styles (e.g. allows ‘)
* #1216 Mark binary serializers as obsolete due to potential security issues in the binary serialization engine of .NET itself (see https://github.com/Catel/Catel/issues/1216)

Added/fixed

(+) #1240 Add support for .NET Core 3.0
(+) #1241 Add IFreezable on ModelBase to allow the object to freeze and protect it from property changes. The ViewModelBase will automatically freeze during closing and unfreeze during initialization
(*) #1192 CanExecute WeakRef is cleared when CanExecute-Lambda is in DisplayClass. This means the Command implementation in Catel will no longer use weak references for the CanExecute function, take extra care for memory leaks and report them if you find them so we can find a working solution
(*) #1242 Reset ViewModelBase.IsInitialized in CloseViewModel to allow later re-initialization
(*) #1244 Ignore loading of resource assemblies to prevent race conditions related to the type cache initialization
(x) #1232 NavigationService.Navigate leads to endless loop when MainPage is MasterDetailPage
(x) #1235 Application-wide commands do not work for UWP apps after upgrade to 5.8.0
(x) #1236 Add missing Catel.MVVM resources to Catel.MVVM.Xamarin.Forms